machine/stm32f103: initial implementation on ADC interface

Signed-off-by: deadprogram <ron@hybridgroup.com>

src/machine/machine_stm32_adc_f1.go

@@ -0,0 +1,108 @@
+//go:build stm32f103
+// +build stm32f103
+
+package machine
+
+import (
+	"device/stm32"
+	"unsafe"
+)
+
+const (
+	Cycles_1_5   = 0x0
+	Cycles_7_5   = 0x1
+	Cycles_13_5  = 0x2
+	Cycles_28_5  = 0x3
+	Cycles_41_5  = 0x4
+	Cycles_55_5  = 0x5
+	Cycles_71_5  = 0x6
+	Cycles_239_5 = 0x7
+)
+
+// InitADC initializes the registers needed for ADC1.
+func InitADC() {
+	// Enable ADC clock
+	enableAltFuncClock(unsafe.Pointer(stm32.ADC1))
+
+	// set scan mode
+	stm32.ADC1.CR1.SetBits(stm32.ADC_CR1_SCAN)
+
+	// clear CONT, ALIGN, EXTRIG and EXTSEL bits from CR2
+	stm32.ADC1.CR2.ClearBits(stm32.ADC_CR2_CONT | stm32.ADC_CR2_ALIGN | stm32.ADC_CR2_EXTTRIG_Msk | stm32.ADC_CR2_EXTSEL_Msk)
+
+	stm32.ADC1.SQR1.ClearBits(stm32.ADC_SQR1_L_Msk)
+	stm32.ADC1.SQR1.SetBits(2 << stm32.ADC_SQR1_L_Pos) // 2 means 3 conversions
+
+	// enable
+	stm32.ADC1.CR2.SetBits(stm32.ADC_CR2_ADON)
+
+	return
+}
+
+// Configure configures an ADC pin to be able to read analog data.
+func (a ADC) Configure(ADCConfig) {
+	a.Pin.Configure(PinConfig{Mode: PinInputModeAnalog})
+
+	// set sample time
+	ch := a.getChannel()
+	if ch > 9 {
+		stm32.ADC1.SMPR1.SetBits(Cycles_28_5 << (ch - 10) * stm32.ADC_SMPR1_SMP11_Pos)
+	} else {
+		stm32.ADC1.SMPR2.SetBits(Cycles_28_5 << (ch * stm32.ADC_SMPR2_SMP1_Pos))
+	}
+
+	return
+}
+
+// Get returns the current value of a ADC pin in the range 0..0xffff.
+// TODO: DMA based implementation.
+func (a ADC) Get() uint16 {
+	// set rank
+	ch := uint32(a.getChannel())
+	stm32.ADC1.SQR3.SetBits(ch)
+
+	// start conversion
+	stm32.ADC1.CR2.SetBits(stm32.ADC_CR2_SWSTART)
+
+	// wait for conversion to complete
+	for !stm32.ADC1.SR.HasBits(stm32.ADC_SR_EOC) {
+	}
+
+	// read result as 16 bit value
+	result := uint16(stm32.ADC1.DR.Get()) << 4
+
+	// clear flag
+	stm32.ADC1.SR.ClearBits(stm32.ADC_SR_EOC)
+
+	// clear rank
+	stm32.ADC1.SMPR1.ClearBits(ch)
+
+	return result
+}
+
+func (a ADC) getChannel() uint8 {
+	switch a.Pin {
+	case PA0:
+		return 0
+	case PA1:
+		return 1
+	case PA2:
+		return 2
+	case PA3:
+		return 3
+	case PA4:
+		return 4
+	case PA5:
+		return 5
+	case PA6:
+		return 6
+	case PA7:
+		return 7
+	case PB0:
+		return 8
+	case PB1:
+		return 9
+	}
+
+	return 0
+}